The NASA mishap investigation board, charged to review
the loss of the X-43A Hyper-X program research vehicle during
its June 2, 2001 launch, concluded no single factor or
potential contributing factor caused the mishap. The flight
failed because the vehicle’s control system design was
deficient in several analytical modeling areas, which
overestimated the system’s margins.

NASA’s Hyper-X program is developing “air breathing” engine
technologies that promise performance benefits for future
hypersonic aircraft and reusable space launch vehicles. In
the X-43A test program, three, 12-foot long, unpiloted
vehicles were planned to fly up to 10 times the speed of
sound to demonstrate scramjet, or supersonic-combustion
ramjet, technologies. The mishap occurred on the first of
three planned flights.

For the launch, the X-43A was attached to the nose of a
modified Pegasus launch vehicle, which was carried by NASA’s
modified B-52 bomber. Seventy-five minutes after takeoff, at
an altitude of approximately 24,000 ft., the Pegasus was
released. Its solid rocket motor ignited 5.2 seconds later
sending the launch vehicle and research vehicle payload on
its test flight. Eight seconds later, the vehicle began its
planned pitch up maneuver, which was expected to take it to
an altitude of approximately 95,000 ft.

Shortly thereafter, the X-43A began to experience a control
anomaly characterized by a roll oscillation. At 13.5 seconds
after release and at an altitude of approximately 22,000 ft.,
structural overload of the starboard elevon occurred. The
severe loss of control caused the X-43A to deviate
significantly from its planned trajectory, and as a result,
it was destroyed by range safety 48.6 seconds after release.

The mishap board found the major contributors to the mishap
were modeling inaccuracies in the fin actuation system,
modeling inaccuracies in the aerodynamics, and insufficient
variations of modeling parameters. The flight mishap could
only be reproduced when all of the modeling inaccuracies with
uncertainty variations were incorporated in the analysis.

“I want to thank the Mishap Investigation Board for their
comprehensive and thorough evaluation,” said Dr. Victor
Lebacqz, acting Associate Administrator for NASA’s Office of
Aerospace Technology. “The findings and recommendations of
the board greatly enhance our opportunity for a successful
second flight,” he said.

Nine chapters of the 11-chapter mishap investigation report
are available to the public. Chapters nine and 10, and
supporting data, are being withheld to comply with U.S.
export control regulations, protection of industry
proprietary information, or for pre-decisional reasons. The
releasable chapters are available on the Internet at:

Related lessons learned from the X-43A mishap investigation
will also be added to the NASA lessons learned information
system, which is available on the Internet at:

For information about NASA and aerospace technology on the
Internet, visit: